The present invention is directed to the field of equipment packaging. It is more particularly directed to shock resistant equipment design and packaging, especially in regard to portable equipment.
It is a constant endeavor to find improved ways of constructing equipment that is resistant to shock. Components mounted within equipment packaged in traditional rigid chassis designs are exposed to high acceleration during shock events generated in normal use and handling. A here-to-fore known solution to reduce the peak acceleration values is to provide a flexible coupling mount with damping and an appropriate sway space for each individual component attached to a common rigid frame or chassis. This is not entirely satisfactory for many packaging applications for which it is being employed.
Portable equipment, and particularly portable computers, have to function in severe shock environments. It is generally desirable and often required that a portable computer be able to survive drops with drop heights between 18xe2x80x3 (45.7 cm) and 32xe2x80x3 (81.3 cm). For example, an IBM L40/SX laptop computer dropped just 12xe2x80x3 (30.5 cm) onto a wooden workbench can experience an acceleration of 1074 g, with pulse durations of 0.3 ms. This acceleration is large enough to damage fragile components such as the disk file, the floppy disk drive and the display.
Mechanical packaging designs of many laptop computer systems are generally based on the properties of stationary equipment. These traditional laptop designs generally employ one of two approaches. The first design approach is to use a rigid chassis or frame. Typically, the chassis is a separate structure provided primarily to support the component devices and to serve as a connecting structure to the supporting floor or table. Some commercial products use this design approach by employing a diecast aluminum frame to support the internally mounted components. A somewhat analogous approach is employed in some other laptop computers. In such computers, the chassis is actually a combination of the case bottom and the printed circuit board. This combination is fairly stiff and does not constitute an energy absorbing design.
The second design approach uses the internal operating components as structural components. There is no chassis per se, and the components are fastened together so as to form the supporting structure. The resulting structure is also quite rigid and is not energy absorbing. In both these approaches, the stiff chassis behaves as a rigid object or elastic, non-dissipative assembly and transmits a received shock to all its components with little or no attenuation. When subjected to the shock, a high acceleration arises from the total system mass colliding with the impacting surface. In the limit of no internal motion, the acceleration is uniform throughout the system. If the system is elastic and non-dissipative very large secondary displacements can result due to the resulting resonances.
A traditional solution is to reduce the acceleration values on a particular costly component only. This is often done for a Direct Access Storage Device (DASD) mounted in a computer. The DASD is provided with a flexible, compliant, and damped coupling shock mount attached to the rigid frame or chassis. This solution also requires that an appropriate sway space be made available. A disadvantage of this design is that the chassis is kept rigid and non-dissipative, allowing unimpeded transmission of received shock pulses throughout the computer structure. This solution also requires that shock protection be provided separately to each component with a customized mounting, with that mounting""s own compliance, damping and mechanical design. This results in a dramatic increase in the number of assembly parts and computer cost.
It is an object of the present invention to provide equipment packages and designs therefor that provide decoupling, damping and shock isolation of motion sensitive components within the package.
In one aspect, the present invention provides an equipment package comprising a flexible shell, a plurality of flexible fillers attached to the shell, and a plurality of objects or components attached to the fillers. Each of the plurality of fillers is formed from a material composition providing flexibility and shock damping to each of the objects. It is desirable for the shell to have a compliance and a damping coefficient matched to the objects.
In another aspect, the present invention provides an equipment package comprised of a flexible chassis, a plurality of objects or components mounted to the chassis to form an assembly, and a plurality of flexible fillers attached to the assembly to form or define the complete package. Each of the fillers is formed from a material composition which provides flexibility and shock damping to each object and provides structural support and integrity for the other objects. In one embodiment, the fillers or the chassis or both are of a laminated construction to achieve the desired anisotropic elastic properties.
It is desirable for the chassis to have a compliance and a damping coefficient matched to the objects. This can be achieved, for example, by varying the thickness of the flexible chassis depending upon location. The nature of the coupling between the objects and the chassis is determined by the resonant frequency and damping involving a particular vibrational mode and particular components.
The invention also provides for at least part of the flexible chassis to have apertures therein that are filled with damping and coupling materials. Alternatively, damping and coupling materials may be selectively attached to the flexible chassis or to the flexible shell. As with the flexible chassis, the flexible shell may be laminated.
Each of the plurality of flexible fillers is formed from a material composition that provides mechanical decoupling, flexibility and shock damping to at least one of the objects such that a shock imparted on a different object is attenuated when received by that object. It is desirable that the material composition includes a foam to keep the weight low and still achieve the desired damping properties. The flexible fillers may be formed of a variety of materials, e.g., laminated, to achieve the desirable anisotropic compliance and damping properties. Such fillers may also have cavities selectively placed therein.
Another aspect of the present invention is a method for making an equipment package comprising the steps of forming a flexible chassis, attaching a plurality of components to the chassis, forming a plurality of damping fillers having predetermined compliance and damping, to substantially fill the spaces between the components in such a manner that the fillers also form the outer surfaces of the package which may optionally be covered with an outer skin. In the flexible shell embodiment, the outer surfaces of the package are formed from the shell material.
One design methodology employs a decoupled simple harmonic oscillator (SHO) model to optimize the shock response behavior. A second design methodology uses a deterministic method (finite element method or FEM) to establish the parameters for the filler and shell materials.